Synchrophaser resetting mechanism for variable pitch aircraft propellers



C. B. BRAHM March 17, 1959 2,877,854 sYNcHRoPx-IASER RESETTING MECHANISMFOR VARIABLE PITCH AIRCRAFT PROPELLERS 2 Sheets-Sheet 1 Filed Dec. 27,1955 INVENTOR A T TORNEY rllnin CHARLES B. BRAHM By ML www; wm ww2,817,854 IABLE C. B. BRAHM SET March 17, 1959 SYNCHROPHASER RE TINGMECHANISM FOR VAR PITCH AIRCRAFT PROPELLERS 2 Sheets-Sheei. 2

Filed DeG. 27, 1955 United States Patent O SYNCHROPHASER RESETTINGMECHANISM FOR VARIABLE PITCH AIRCRAFT PROPELLERS Charles B. Brahm,Windsor Locks, Conn., assignor to United Aircraft Corporation, EastHartford, Conn., a corporation of Delaware Application December 27,1955, Serial No. 555,596 18 Claims. (Cl` H0-135.29)

This invention relates to phasing mechanism for two or more devices andparticularly to phasing mechanism for maintaining two or more rotatingaircraft propellers substantially in a selected phase relation.

An object of this invention is mechanism for limiting the extent ofchange of the slave governor by the master device and means fortemporarily disabling control by the master and recentering the slavegovernor control.

A further object is mechanism for electrically returning a control motorto a central position upon disabling of its control signal.

A still' further object is means for recentering a portion of a controlmechanism while holding the controlled device in a substantially fixedposition.

Another object is mechanism lfor electrically returning a governor speedsetting control motor to a central position while holding the governorspeed setting substantially iixed and then again connecting the centeredcontrol motor with the governor speed setting mechanism.

Further and other objects will be apparent from the followingspeciication and the attached drawings in which:

Fig. l is a block diagram showing one master unit and one slave unit andmeans for interchanging the master and slave and also indicating howadditional slaves may be added.

Fig. 2 is a schematic wiring diagram of the synchronizer and phasingportion of the electronic control schematically showing three slaves andshowing one sampler in detail and how it is connected to the two-phasemotor.

Fig. 3 is a diagram showing the stop for the governor control,

In the operation of multi-engine aircraft it has been found desirableboth from a vibration and a noise standpoint to not only synchronize theseveral enginedriven propellers but to also maintain a selected phaserelation between the propellers. Mechanism responsive to speed alone isnot capable of maintaining the required phase relation even when suchmechanism is capable of maintaining speed synchronization.

Applicant has invented an improved device which may be used to controlthe speed `of each propeller independently with the synchrophasingmechanism disconnected or may be able to synchronize the severalpropellers, selecting one as a master and the others as slavessynchronized with the master and maintain a selected phase relationbetween the master and slave within comparatively small limits with thesynchrophasing mechanism connected. The type of propeller which has beenchosen to explain the synchrophaser mechanism is the type similar tothat shown in iedrziewski Patents Nos. 2,704,583, issued March 22, 1955,and 2,636,566, issued April 28, 1953. In this propeller type, which isnow well known in the art, a hydraulically actuated piston mounted in adome on the forward part of the propeller is actuated by hydraulic liuidcontrolled by a iiyball governor similar to that shown in rPatent No.2,636,566 to 'change the propeller pitch. The speed setting of the ricegovernor is obtained by adjusting the position of one end of the speederspring of the governor. In the present embodiment, the spring isadjusted by an electric motor in a manner similar to that described inMartin Patent 2,252,518, issued August 12, 1941, by a step-motor andcontrol similar to that shown in Drake Patent No. 2,327,341, issuedAugust 24, 1943. Reference may be made to the above mentioned patentsfor further details of the propeller, the propeller governor, andgovernor spring setting means. As this mechanism is generally wellknown, it is believed that further explanation will not be necessary fora complete understanding of the present invention.

As shown in the Drake patent, the governor setting motor of the presentapplication is a step-motor controlled by a commutator switch. Thestep-motor will turn in one direction or the other depending upon thedirection of rotation of the commutator switch or the polarity appliedto the commutator switch.

In the present embodiment, the commutator switch in each of the slavedevices is driven by a two-phase motor which is controlled by theelectronic synchronizing and phasing mechanism which compares the speedand phase of the master and slave devices. The commutator switch for themaster motor is driven by a manually controlled D. C. motor so that themaster motor governor may be set at any desired speed setting.

Provision is also made for substituting manually controlled commutatorswitches, shown generally at 33, Fig. l, for the master or slavecommutator switches so as to manually control any one or all of theseveral rotating devices at will.

The syncronizing and phasing mechanism comprises individual meansproducing a pulse in timed relation to the rotation of the respectivedevice and mechanism converting the pulse from the master into asaw-tooth wave timed with said pulse. The saw-tooth wave is sampled bythe pulse from the slave and a signal proportional to the value of thesaw-tooth at the instant of sampling is produced. The value of thesignal indicates the phase relation between the master and the slave, azero signal indicating an irl-phase relation. If the slave and masterare operating at different speeds, an additional oil-speed signal may beproduced. The off-phase and oli-speed signals are combined, chopped,ampliiied and fed to a two-phase motor which drives the commutatorswitch of the slave to return the slave to synchronism and phase.

lt has been found that the electronic control can control the governorspeed setting accurately enough so as to maintain the phase relation oftwo or more devices, such as master and slave devices, to within a verysmall range such as l() degrees by controlling the Speeder springs ofthe various governors with the speed and phase sensitive electroniccontrol hereinafter described.

As shown in Fig. 1, a master engine 10 drives a proeller 12 whose pitchis controlled by a governor 14 having a step-motor 16 for adjusting thesetting of the Speeder spring of the governor. The step-motor 16 ismotivated by rotation of commutator switch 13 rotated by a D. C. motor20 controlled by a switch 22 so as to set the master governor speed whenengine 10 and propeller 12 are utilized as the master.

Slave engine 24 drives propeller 26. The pitch of propeller 26 iscontrolled by a iiyball governor 28 whose Speeder spring may be set bythe step-motor 30 controlled by a commutator switch 32 rotated by atwophase motor 34 which is controlled by the electronic synchronizingand phasing mechanism described hereinafter so as to adjust the Speederspring of governor 28 to maintain the engine and propeller 24, 26 insynchronism and in phase with the master vengine and propeller 10, 12.

Switching,mechanismwhich will be described hereinafter is provided forinterchanging controls so as to optionally utilize engine 24 as themaster and engine 10 jas a slave.y Switching mechanism 33 is alsoprovided for manually operating any of the governor setting mechanisms.Although only one system 33 for substituting manually controlledcommutator switches has been shown, it will be understood that eachslave and the master will generally be provided with such a system. Theadditional systems have been omitted for the sake of drawing simplicity.

The synchrophasing mechanism comprises a pulse generator for eachdevice, two lof which generators, 36 and 76, are shown in Fig. 1. Eachpulse generator is similar to thatshown in an application Serial Number555,595 of Stanley G. Best for Synchronizer tiled on even date .herewithto which referencemay be made for a more detailed description. ItAshould be suflicient here to state -that this pulse generator comprisesa permanent magnet anda coil which are moved relative to each other bythe propeller and once each revolution pass in close proximity so as tocreate a pulse having a positive going portion in the coil.

The free end of the coil of pulse generator 36 is grounded or connectedto a common return line and the other end is led through aline 38, to Aasaw-tooth former 40 and there the pulse is transformed into a saw-toothvoltage wave. As shown in Fig. 2, saw-tooth former 40 .has a transformer42 which steps-up the voltage of the pulse. The amplified pulses arethen led through the Ielectronic circuits-including a tube 44 and a tube46 .where they are transformed into a linear saw-tooth wave.

-ceven date herewith, so that the following brief explanation of thesaw-tooth former structure here is believed all that will be necessaryto understand the present invention. The pulse developed by the masterengine pulse generator 36 is coupled via condenser 43 to the signal grid50 of the cathode-follower tube 44. When the pulse causes the bias ongrid 50 to be less than cut-off, tube 44 will conducty and negativelycharge condenser 52 close to the negative cathode potential of the tube44. Resistors 54 and 56, forming a voltage divider from the negativevoltage, say minus 160 volts, of rectifier 59, place a negative voltageon the cathode 60, which is normally slightly positive with respect tothe grid S so that tube 44 is normally non-conducting. Capacitor 62serves as a by-pass to prevent any rapid change in cathode currentappearing as a bias von the tube. Condenser 52 is discharged to a lessnegative voltage through resistors 64 and tube 46.

Resistor 66 is a cathode resistor of tube 46 which is a cathode-followertype of tube having a plate voltage of say plus 200 volts supplied bythe rectifier 58. As the grid of tube 46 is grounded through gridresistor 7d, the average grid voltage is zero with respect to ground sothat the average current through tube 46 is constant and hence theaverage voltage appearing at the junction or resistors 64 and 66 hassome average value between minus 160 volts and plus 200 volts, sayaroundzero volts with respect to ground. Hence, condenser 52 will charge tosome negative value of say 140 volts when tube 44 conducts, and will bediscarded slowly through resistors 64 and tube 46 to a xed amount lessthan the voltage at their junction with resistor 66, say 70 volts less,during the period when tube 44 is not conducting. This will produce avoltage across the condenser 52 which will be of the desired saw-toothform. As explained in more detail in the Oifner patent and the abovementioned application, the saw-tooth curve will be a linear curve and-will not .vary .materially with frequency. Due to the cathode followeraction and the variation of the grid voltage of tube 46 with variationin the charge on con denser 52, a linear saw-tooth wave, varying bothsides of zero voltage, is produced at the junction of resistors 64 and66.

The linear saw-tooth voltage from the saw-tooth former 46 is led on line72 to a sampler 74 where it is sampled by a pulse from pulse generator76 of propeller 26 to give a proper signal to the two-phase motor 34 toadjust the governor of the propeller 26 in accordance with the speed andposition of the propeller 12. Sampler 74, as shown in Fig. 2, has acircuit comprising tubes 78 and`80 having the cathode of the tube 7S andthe plate of tube 8i) connected to the saw-tooth input by line 82. Thepulse from the pulse generator 76 of the slave engine is fed in on line84 to a transformer 86 and thence to the grid of both tubes 78 and 8l).A negative bias with respect to ground is normally maintained on bothgrids by the resistors 8S and 90 forming a voltage divider and connectedto the minus 160 volt line. The positive going portion of the pulse fromgenerator 76 applied to the grids of tubes 7S and 80 will cause one ofthe tubes 73, Sil to conduct and charge condenser 92 and thus sample thesaw-toothvoltage and place a resultant signal on the grid of tube 94which will indicate the direction and extent of out-of-phase of themaster with respect to the slave. The fixed grid bias on thefgrid oftubes 73 and 80 is so adjusted that no anode current can flow througheither tube, except when the positive going pulse is applied to thegrids from the slave pulse generator.

If at the time the positive going pulse is applied to the grids of 78and Sil the saw-tooth wave from the master applied to tubes 78 and Silis positive or more positive than the charge on condenser 92, then tubewill conduct and charge condenser 92 to a more positive value. If at thesampling instant the condenser were more positive or less negative thanthe saw-tooth wave from the master, then tube 78 will conduct and reducethe charge on the condenser. Thus a phase dierence voltage Wave will bedeveloped across an energy storage device such as condenser 92 whichwill have a polarity and magnitude indicating the magnitude anddirection of any out-of-phase relation between the master and the slave.No signiiicant current will flow from the condenser 92 to the grid oftube 94.

Tube 94 being a cathode follower type will, at the contact ofpotentiometer 96, give an indication in line 98 of the out-of-phasecondition. With no grid signal, i. e., zero voltage with respect toground, on tube 94, a zero voltage will be obtained in the potentiometer96. The wiper arm will be set so as to give this zero voltage -for theon-phase condition. When the slave propeller is leading, the slave pulsewill sample a negative portion of the saw-tooth to give a negativevoltage on the grid of tube 94 and cause the voltage detected by thepotentiometer 96 to become negative. The voltage from the potentiometer96 is led through a resistor 109, and a lead network 192 to a lagnetwork 194 and a resistor 106. Resistor 106 is connected throughresistors 108 and 110 to a chopper 112 and an amplifier 114. The chopper112 is energized from the ships supply, which may be a 400 cycle 1l5volt supply through transformer terminals 116 and 118. The amplifier isa push-pull amplifier which will amplify the 400 cycle square waveproduced by the chopper 120 and transmit it to the control Winding 120of the two-phase motor 34 used to actuate the commutator switch 32 andadjust the propeller pitch. The reference winding 122 of the twophasemotor 34 is energized directly from the 400 cycle ships supply.

The chopper 112 has a mechanical lag which will provide the input signalsupplied to amplier 114 with a 70 degree lag with respect to the supplyvoltage. The transformer 124 may be tuned to provide additional lag sothat the control voltage supplied to the-winding of the two-phase motor34 will have about a 90 degree lag behind the reference voltage supplyto the winding 122 which will cause the motor 34 to rotate in onedirection.

Upon a change in polarity of the D. C. voltage supplied to the chopper112 and the amplifier 114, the control voltage in winding 12) will haveabout a 90 degree lead over the reference voltage in winding 122 andwill cause the motor 34 to rotate in the opposite direction. Thus, thegovernor setting of the slave may be changed to increase the slavepropeller speed if the slave is lagging, `and decrease the slavepropeller speed if the slave is leading to thereby bring the slavepropeller back into phase with the master.

If it is desired to change the phase relation of the master and slave soas to cause the slave to lead or lag the master by a given amount, thesignal from the phase output 96 is modified by a signal applied atjunction 126. This signal is supplied from a manually actuated phasecontrol potentiometer 128 having its own power supply from terminals 130and 132 of power transformer 134 and its own rectifier 136. Thus, if thephase output 96 is providing a negative signal at the junction 126 dueto a phase lead of the slave and a positive signal is supplied frompotentiometer 128 through resistor 138 to the junction 126 which willresult in a zero voltage at that junction, no signal will be supplied tochange the slave governor setting and the slave will continue to operatein this phase lead position and the synchrophaser will Work in itsnormal manner to maintain this relationship.

In a manner more fully described in the above identified application towhich reference may be made for a more detailed description, if therelative position of the propellers were to change by more than 180degrees from the zero-signal, in-phase position, an erroneous signalwould be obtained. For instance, if the slave were running faster thanthe master, the ofi-phase signal would be negative as the slaveincreased its leading position tending to reduce the slave speed untiljust after the end or bottom of the saw-tooth wave was sampled, at whichtime the sampled portion of the saw-tooth would change polarity and bepositive and the olf-phase signal would also be positive. Although theslave would still be running faster than the master, it would in effecthave a lagging position with respect to the master and thus give anofi-phase signal in the opposite direction from that in which thecorrection should be made. ln order to solve this problem, an oft-speedintegrator is supplied which will count the number of revolutions ofoff-phase as they are passed and produce a signal of the correctpolarity proportional to that number, which signal is added to theoff-phase signal and applied to the amplifier to give a speed correctionin the proper direction. The off-speed integrator utilizes the suddenvoltage change in the sampled saw-tooth Wave voltage to produce a pulsein the plate circuit of tube 94 and energizes cathode follower tube 140to produce an off-speed signal at the wiper of potentiometer 142. Thevoltage from wiper 142 is led through a limiter 144 and combined atjunction 146 with the oft-phase voltage signal.

In this ott-speed integrator, if a condenser is charged every time theabrupt change in the sampled saw-tooth voltage occurs and the charge didnot materially leak off the condenser between changes, the voltageacross the condenser would indicate the number of times and thedirection the relative phase had gone through 180 degrees. If the phasewere changing in one direction, i. e., the slave underspeeding, thecharge on this conf denser would continually be going positive to effectan increase in speed. If the phase were changing in the other direction,i. e., the slave overspeeding, the voltage across this condenser wouldcontinually be going negative to decrease the speed. When this voltageis added to the oft-phase signal, theeffective range of synchropliasingiS thus extended beyond 'the 180 degrees relation.

The signal for the grid of tube is obtained by placing a resistance 148in the plate circuit of tube 94. For an overspeed of the slave, therewould be a voltage change in the negative direction across resistance148 caused by the positive going pulse on the grid of tube 94 induced bythe abrupt positive going change in the saw-tooth voltage. The negativevoltage change across resistance 148 is coupled through condenser 150and rectifier 152 charging condenser 154 to some more negative valuethan it had previously achieved. This more negative value is applied tothe grid of tube 140. Each pulse charging condenser 154 is additiveuntil a maximum is reached, and thus each additional charge drives thegrid of tube 140 more negative to decrease the current in cathoderesistor 156 and decrease the voltage at junction 146. The potential atthe wiper 142, due to the cathode follower action, will be almost thatexisting across condenser 154. This negative cathode voltage is appliedto the junction 158, thus tending to maintain the charge on condenser154. Resistors 160, 162, 164, and 166 serve to bias rectiiers 152 and168 so that no con duction will occur in tube 148, except when amaterial change in voltage occurs at the plate of tube 94. The sizes ofthe condensers and 170 are such and the contact potential of rectifier-s152 and 168 are such that an abrupt material change in voltage isrequired to make the rectifiers conduct. Thus, a slow change in phasebetween and 180 will not charge condenser 154, but when the phasecircuit goes through the 180 mark an abrupt and material change willoccur and charge condenser 154 to some new value.

The action for an underspeed condition of the slave is exactly the same,except that all polarities of signals are reversed and rectifier 168conducts, biasing the grid of tube 150 more positively.

The convention used in this application, with respect to rectiers, isthat the arrows indicate current iiow, as opposed to electron flow. Thecontact potential of the rectifier in limiter 144 is such that noconduction will occur for small changes in the cathode follower outputat the wiper 142.

The lag network 104 serves as an integrator to obtain high staticsensitivity by blocking the flow of D. C. signals to ground while stablecontrol is still possible because of reduced dynamic sensitivity. Thelead network 1432 assists in dynamic stability by passing rapidlychanging signals.

Each two-phase motor drives an individual potentiometer and, as shown inFig. 2, two-phase motor 34 for example, there being similar motors foreach slave, drives a potentiometer 172 which will feed a signal backthrough resistor 174 to junction 176, where it is combined with theoff-phase and off-speed signals, The potentiometer 172 is provided witha voltage from the rectifier 136 and the power transformer 134. Theoutput of the potentiometer ranges from negative to positive, dependingupon its position.

As shown in Fig. 3, two-phase motor 34 taken as an example is connectedthrough a gear reduction to a stop mechanism comprising a slotted gear178. A fixed pin 180 rides in slot 182 and limits the extent of motionof the two-phase motor 34. As the two-phase motors, such as 34, drivethe commutator switches to reset the mechanical governors, limiting themotion of the two-phase motors will limit the extent to which thegovernors may be reset. In a practical embodiment, this resetting of thegovernor by the phasing mechanism has been limited to approximately 3percent of the governor speed so that upon failure of a master, theslave cannot be reset more than 3 percent by the phasing andsynchronizing mechanism in attempting to follow the master.

The potentiometer 172 is connected with the two-phase motor 34 so as togive a zero voltage when the motor is in its central position; that is,when fixed pin 180 is in the midpoint of slot 182.

As to the two-phase motor 34 makes a correction in 7 speed setting tocompensate for au off-phase signaL'the potentiometer 172 is actuated tooppose that off-phase signal. Resetting of the governor by the two-phasemotor 34, working through the commutator switches, will also tend toreduce the off-phase signal by bringing the slave nearer into phase withthe master and eventually the point is reached where the feedback signalis equal to or greater than the ott-phase signal. When the feedbacksignal becomes greater than the off-phase signal, the two-phase motorwill start operating in the opposite direction to reset the slavegovernor with the propeller continuing to correct toward the on-phasecondition. With both the feedback signal and the otfphase signaldecreasing, the two-phase motor will come to rest at its center positionwith the propeller on-phase and with a zero sampler or orf-phase signal.It will be noted that the original setting is ultimately desired in thecase where merely a phase correction is being made, because the enginespeeds are already equal, and correction is necessary only temporarilyuntil the slave is vbrought into phase, at which' time the originalspeed setting is again desired in order to maintain the speed matchingin the new phase relationship.

In the event of an off-speed condition which will require a resetting ofthe slave governor to change the slave speed to maintain synchronismwith the master, the two-phase motor will nally come to rest otf thecenter position wherever a balance is achieved between the potentiometerfeedback and the off-phase or off-speed signal. If the originalott-speed were small, the sleeve engine will have been brought into aphase leading or lagging position where the speed of the slave and themaster are the same but the off-phase signal will be balanced by thepotentiometer feedback due to an offcenter .position of the two-phasemotor and with the slave governor set at a phase somewhat different thanits manual setting. Under these conditions, the resynchronizing button184, Fig. l, may be actuated, or the phase control potentiometer may beset to accomplish the desired phase matching between master and slave.The resynchro-nizing button 184 supplies 28 volts D. C. to a relay 186which, when de-energized, will connect junction 146 and similarjunctions on each of the other channels with ground thus preventing anysignal being fed to the amplifiers and the two-phase motors. Theresynchronizing button 184, also supplies 28 volts to relay 188 or 190,depending upon the position of the master selector switch 192. As shownin Fig. 1, propeller 12 has been selected as the master so that relay188 is controlled by resynchronizing button 184. De-energization ofrelay 188 will transfer control of the governor setting motor 38 to themaster commutator switch 18 and thus hold the slave governor at thesetting that it had at the time the resynchronizing button was actuated.

By grounding the junction 146 by relay 186, the signals from thepotentiometer 172 alone, are fed back to the chopper 112 and theamplifier 114 to actuate the two-phase motor 34 and restore it to acentral position where there will be no feedback from the potentiometer172. The resynchronizing button 184 can then be released and the variousslaves restored to control by their respective two-phase motors. Asshown in dot-anddash lines in Fig. 1, additional slaves besides the twoshown in Fig. 1, may be controlled by the resynchronizing button 184. Ifthe governor settings of the slave and the master are materiallydifferent, more than one `actuation of the resynchronizing button may benecessary j to bring the propellers into an on-phase position.

Master selection switch 192 controls relay 194 tointerchange theconnections of the pulse generators and the commutator switches of twoof the devices to thereby change a -slave to the master, andthe masterto a slave.

Opening of the main switch will place the'control of Iall of the deviceson the master commutator switch 18. Additional commutator switchesactuated by manually controlled D. C. motors may be substituted at anytime yfor either the master or slave commutator switches, as shown atl33 in Fig. 1. Although this manual control has been shown only inconnection with the master motor, it is obvious that similar comutatorswitches may be connected to the individual step-motors in the governorsand their synchronizing step-motors disconnected.

It is to be understood that the invention is not limited to the specificembodiment herein illustrated and described, but may be used in otherways without departure from its spirit as dened by the following claims.

I claim:

1. In a governor system for independently rotating devices, meansproducing an electrical signal indicating a difference in an operatingcharacteristic between two of said devices, a motor operativelyconnected with one of said devices for adjusting the speed of said oneof said devices to eliminate said diterence, means directing saiddifference signal to said motor for controlling the operation of thesame, said motor having a central position, means producing anoff-center signal responsive to movement of said motor from said centralposition, and means, including means responsive to said oif-centersignal, for returning said motor to its central position and includingmeans preventing adjustment of the speed of said one device relative tothe other during said return.

2. In a governor system for independently rotating propellers havingpitch adjusting means, means producing an electrical signal indicating adiierence in speed between two of said propellers, a motor operativelyconnected with the pitch adjusting means of one of said propellers foradjusting the speed of said one of said propellers by changing the pitchof said one propeller to eliminate said difference, means directing saiddtference signal to said motor to control the operation of said motorand the pitch adjusting means of said one propeller, said motor having acentral position, means producing an off-center signal responsive tomovement of said motor from said central position, and means includingmeans responsive to said off-center signal for returning said motor toits central position, and including means disconnecting said motor fromthe pitch changing means of said one propeller.

3. A device as claimed in claim 1 in which the operating characteristicis speed.

4. A device as claimed in claim 1 in which the operating characteristicis phase.

5. In a governor system for independently rotating de- -vices in whicheach device has its own speed governor and means actuated by eachgovernor for adjusting the speed of the respective device, meansproducing an electrical signal indicating a difference in an operatingcharacteristic between two of said devices, a motor opera- `tivelyconnected with one of said governors for adjusting the speed setting ofsaid one of said governors to eliminate said difference, means directingsaid ditference signal to said motor to contro1 the actuation of thesame, said `motor having a central position, means producing anyoff-center signal responsive to movement of sald motor from saidcentral position, and means including means responsive to saidoff-center signal for returning said motor to its central position saidreturning means including means preventing adjustment of said onegovernor relative to the other during said returning operation.

6. A system as claimed in claim 5 in which said preventing meansincludes means connecting both governors with the sameadjusting means. Y

, 7. A system as claimed in claim 6 in which said other device hasamotor for adjusting its speed and said same adjusting -means is theadjusting motor for said other device.

8. Asystem as claimed in claim l including means limiting the movementof said motor from its central position to a preselected amount, tolimit the effect without actuation of said returning means toapproximately 3% of the speed of said one device.

9. In a governor system for independently rotating devices to bemaintained in a selected relation, means actuated by an operatingcharacteristic difference between two of the devices creating adifference signal, means creating from said dilerence signal a signalalternating voltage having approximately 90 phase displacement from areference alternating voltage, a two phase motor connected with andenergized by said alternating voltages, said motor having a centralposition and operatively connected with one of said devices foradjusting the speed of said one of said devices to eliminate saiddifference as it moves from said central position, means, responsive tomovement of said motor from said central position, producing anoff-center signal, connected with and opposing said difference signal,means disabling said signal alternating voltage and creating from saidoit-center signal a third alternating voltage having approximately 90phase displacement from said reference voltage, means electricallyconnecting said third alternating voltage with said motor for returningsaid motor to the central position, and means preventing adjustment ofthe speed of said one device relative to the other during said returnmovement.

10. A governor system as claim in claim 9 in which the difference signalis a D.C. signal, and said off-center signal is a D.C. signal, and saidsignals are of opposing polarity and are combined and fed into anamplifying system to convert them to an A.C. signal for operation ofsaid two-phase motor.

11. A governor system for a plurality of independently rotating devicesto be maintained in a selected phase relation, means producing anelectrical signal indicating the phase difference between said devices,a motor operatively connected with one of said devices for adjusting thespeed of said one of said devices, means directing said phase differencesignal to said motor for controlling the operation of the same, saidmotor having a central position and means actuated by said motorproducing an ot`fcenter signal proportional to the ofi-center positionof said motor, means blocking said phase different signal from saidmotor and disabling the adjusting ability of said motor and means,including means responsive to said oli-center signal connected with saidmotor for returning said motor to its central position.

12. A governor system for a plurality of independently rotating devicesto be maintained in a selected phase relation, comprising an individualiiyball governor for each device, a Speeder spring for each governor,individual means for adjusting each said spring to select the speedsetting of the respective governor, means actuated by each governor forcontrolling the speed of the respective device, a pulse generator foreach device operatively connected with the respective device to producea pulse in timed relation to the rotation of said respective device,means comparing the pulses of two of said devices and producing anelectrical signal indicating the phase difference between said devices,a motor connected with said adjusting means, means directing said phasedifference signal to said motor for controlling the operation of thesame, said motor having a central position and means actuated by saidmotor producing an oit-center signal proportional to the oft-centerposition of said motor, means directing said olf-center signal to saidmotor in opposition to said phase difference signal, means blocking saidphase difference signal from said motor, and disconnecting said motorfrom said adjusting means and means, including means responsive to saidott-center signal, for returning said motor to its central position.

13. A phasing system for a plurality of rotating devices including amaster and a slave, each having means creat ing an electrical pulse intimed relation to the rotation of the respective device, electric meansenergized by said pulses due to a phase difference between said masterand slave and creating a signal alternating voltage having approximatelyphase displacement from a reference voltage, a two-phase motor energizedby said alternating voltages, a governor controlling the speed of theslave device, means connecting said motor with said governor forchanging the speed setting of said governor, means actuated by movementof said motor from a central position for creating a signal opposing thesignal which created the movement, means for disabling said signalalternating voltage and utilizing said opposing signal to return saidmotor to its central position.

14. A system as claimed in claim 13 in which said electric meansincludes means producing a D.C. signal responsive to said phasedifference, and said means connecting said motor with said slavegovernor includes a commutator switch and a speed setting motorcontrolled by said switch, said system including a governor for saidmaster and a master commutator switch and switch actuator and a speedsetting motor actuated by said master switch for setting said mastergovernor, said means creating said opposing signal producing a D.C.signal of a polarity opposite to said phase difference D.C. signal,means for combining said D.C. signals and leading the resultant signalto an amplifying system transforming said resultant D.C. signal to saidsignal alternating voltage, means disabling said phase difference signaland transforming said opposing D.C. signal to an A.C. signal to actuatesaid motor, and means disconnecting said slave governor setting motorfrom its commutator switch and connecting it with said master commutatorswitch during return of said motor to its central position.

15. A system as claimed in claim 5 including electrically actuatedgovernor speed setting means for said one governor, a commutator switchdriven by said motor electrically connected with said electricallyactuated means for controlling the operation of said speed settingmeans, and causing the same to follow the direction and extent ofoperation of said switch.

16. A system as claimed in claim l5 including electrically actuatedgovernor speed setting means for said other governor, a second motor, asecond switch driven by said second motor, and means electricallyconnecting said second switch with said other governor to control theoperation of said other governor speed setting means following thedirection and extent of operation of said second switch.

17. A governor system as claimed in claim 2 including means limiting themovement of said motor from its central position to a preselectedamount.

18. A system as claimed in claim 16 in which said preventing meansincludes means connecting both speed setting mechanisms with said secondswitch, and discon necting said one governor switch from its speedsetting mechanism.

References Cited in the tile of this patent UNITED STATES PATENTS2,431,687 Drake Dec. 2, 1947 2,482,812 Treseder Sept. 27, 1949 2,513,222Wilson June 27, 1950 2,517,703 Oner Aug. 8. 1950 2,673,309 Light et al.Mar. 23, 1954 2,747,141 Hine May 22, 1956

